1. Field of the Invention
The present general inventive concept relates to an image forming apparatus, and more particularly to an image forming apparatus having a power transmission device that intermittently transmits power to a plurality of driven bodies from a driving source.
2. Description of the Related Art
An image forming apparatus is an apparatus that prints an image on a printing medium, e.g., paper, according to an input image signal. One type of image forming apparatus is an electrophotographic color image forming apparatus, which is configured such that a beam is scanned across a photosensitive body. The photosensitive body is charged with a predetermined electric potential to form an electrostatic latent image on the outer peripheral surface of the photosensitive body, the electrostatic latent image is then developed into a visible image by supplying toners to the electrostatic latent image, and the visible image is transferred onto and fixed to paper. Typically, toners of four colors of yellow (Y), magenta (M), cyan (C), and black (K) are used in the color image forming apparatus, and thus four developing devices corresponding to the respective colors are required.
Various rotating bodies, including photosensitive bodies and developing rollers, are mounted to the developing devices, and the rotating bodies are driven by one or more driving sources provided in the image forming apparatus.
In order to save on the cost of components, generally the number of motors used is as small as possible. Thus, in many cases, a plurality of developing devices are driven by one motor. The single motor either drives only one of the developing devices, drives all the developing devices at the same time, or drives all the developing devices in sequence. To achieve this, a power transmission device is mounted on a path through which the power from the motor is transmitted to the developing devices. In some circumstances, the power transmission device transmits power to only the developing devices that are to be driven, and interrupts power to the developing devices that do not need to be driven.
An example of a conventional image forming apparatus having the above power transmission device is disclosed in Korean Patent Registration No. 636217, which includes two electronic clutches and one solenoid to intermittently transmit power to a plurality of developing devices.
However, the disclosed conventional power transmission device is uneconomical because it requires at least two electronic clutches which are expensive, and is limited in that it cannot be utilized in a compact image forming apparatus because the size of the electronic clutch is increased as a result of an increase in the driving loads of the developing devices.
Further, electric current is continuously applied to the electronic clutch to transmit power. Accordingly, when successively transmitting power over a long period of time, heat is generated from the electronic clutch, causing deterioration in the performance of the electronic clutch, and consequently the electronic clutch malfunctions.